In general, there are well known some mechanisms for preventing an oxide film from being formed on the surface of each of the semiconductor substrates whenever the semiconductor substrates are put into and out of a heat treating apparatus. For example, a substrate space through which the semiconductor substrates are put into and out of the heat treating apparatus is isolated from an external air and further evacuated into a vacuum, before the semiconductor substrates are put into and out of the heat treating apparatus. As a result, it is possible to prevent an oxide film from growing on the surface of each of the semiconductor substrates.
In the above-mentioned conventional method, although the growth of an oxide film on the surface of each of the semiconductor substrates due to the external air can be suppressed, it is impossible to suppress the growth of an oxide film due to moisture absorbed in the semiconductor substrate naturally. In addition, it is impossible to remove an oxide film formed between when an oxide film on each of the semiconductor substrates has been removed and when the semiconductor substrates are put into the heat treating apparatus.